Thick crowds poured onto the grounds of Munich's Oktoberfest today despite a bomb explosion last night that left 12 dead, 144 injured and few hard leads for the police.

Munich authorities, who had considered cutting short the famous beer fest midway through its two-week run, announced instead that the fair would be closed only on Tuesday for a day of mourning for those hurt in the blast.

The Oktoberfest's carnival blend of great drinking halls and outdoor amusements has drawn foreigners from around the world since it was established in 1810.

Among those dead who have been postively identified are one Briton, one Swiss, two Austrians and five West Germans, including three children. One Bavarian official said there was no indication that any Americans were among the victims.

Government officials offered a reward of $55,000 for information leading to those responsible for the attack. Police reported having received about 70 anonymous tips, including one linking the bombing to a group that claimed responsibility for an August bombing in Bologna, Italy, that left 84 dead.

The atack, West Germany's worst postwar bomb explosion, thrust the issue of security into the minds of West Germans three years after the last major terrorist action and one week before national elections.

For months police have been warning against a possible resurgence of terrorist activity in West Germany expressly intended to influence the election. The theory has been that terrorists would want to bring off a major coup to cause a rightist backlash, which would usher into power the right-of-center opposition candidate for chancellor, Bavarian state premier Franz Josef Strauss.

Under Strauss, so the theory goes, the left would be united and terrorism would flourish because its practitioners would claim to be fighting a fascist state.

Still, some police officials tended to discount leftist responsibility for the explosion yesterday, noting that such mass attacks resemble more closely the tactics of rightist groups.

In line with this, the West German mass-circulation paper Bild am Sonntag reported that the first phone call it received after the explosion was from a woman who, speaking bad German in a French accent, claimed right-wing extremists were responsible for the Oktoberfest bomb.

"We are of the right wing from Bologna," she said. "We are against the reds. We made the attack yesterday. We will continue."

While West German authorities were unprepared yet to credit any group with the attack here, Bavarian Interior Minister Gerold Tandler said the bomb seemed to be the work of "a professional." Sources described it as a cast-iron tube, less than an inch wide, filled with two to six pounds of explosives that were electronically triggered.

The bomb exploded at 10:18 p.m. in a green waste bin located at the main entrance of the fairgrounds. Coming a short time before the beer halls closed, the attack was timed for peak exit period.

Observers reported the explosion sent a sheet of flame 40 feet into the night sky and could be heard for blocks. There was panic, screaming and weeping, they said.

But 12 hours later when the festival grounds reopened, the charred entrance scene had been washed clean with water hoses and new flagstones were already cemented in place where the bomb had gouged a deep crater.

On the sidewalk, wreaths of flowers were placed by unknown persons. A note was attached that read, "People died here yesterday. If you still want to visit the Oktoberfest, then remember that children, women and men were torn to shreds where you are now standing."

With Munich filled by 600,000 visitors, Mayor Erich Kiesl said in a television interview that he had been reluctant to close the Oktoberfest, leaving crowds stranded.

Although many attending the festival said they were saddened by yesterday's tragedy, the prevailing sentiment appeared to be for the fair to continue until its normal conclusion Oct. 5.

"The show must go on," said Hermann Wandesleben, a Munich insurance agent. "If we stop it now, then we come under the influence of violence like this. We are upset, we are angry. But it is like the 1972 Olympics here [in which Israeli athletes died in a Palestinian terrorist attack]. Those Games continued too."